Control of grapevine diseases, including downy mildew (Plasmopara viticola) and Asian grapevine leaf rust (Phakopsora meliosmae-myrianthae) in the main grape-growing regions of Brazil has been achieved using foliar fungicide applications programmed at fixed intervals. A survey conducted with table grape growers from Northwest São Paulo State showed that the number of fungicide applications has been excessive both in European cultivars (Vitis vinifera) and American cultivars (Vitis labrusca), with averages of 103 and 59 applications per crop cycle, respectively (Costa et al., 2012). This excessive frequency of fungicide applications leads to an increase of production costs and risks of selection of resistant organisms, thereby compromising the efficiency of chemical control. Information about the sensitivity of these important pathogens to Quinone outside Inhibitors (QoIs) and Demethylation Inhibitors (DMIs) fungicides are scarce in Brazil. Sensitivity monitoring of P. viticola and P. meliosmae-myrianthae isolates to the main single-site fungicides used in the country has been performed using in vivo and in vitro tests (FAPESP 2017/21412-6), and isolates with different sensitivity levels were detected. To better understand the results from those studies, molecular analyses are necessary to identify the underlying fungicide resistance mechanisms in these pathogens. Molecular analyses including sequencing of cytb and cyp51 genes, quantification of cytb G143A in populations and expression analysis of cyp51 in individual strains will be carried out at Rothamsted Research under the guidance of Dr. Bart Fraaije and Dr. Nichola Hawkins. Results obtained from in vivo, in vitro and molecular studies will help to rationalise a fungicide-resistance management program for the main grapevine diseases in Brazil.
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